The present invention relates to an electrophotographic recording material comprising an electrically conducting layer support particularly suitable for the production of printing plates or printed circuits, and a photoconductive layer comprising an organic photoconductor, a phenolic resin as the binder, a sensitizer and customary additives.
A recording material of the above type is known (German Patent No. 25 26 720, equivalent to U.S. Pat. No. 4,063,948). Binders are included in this photoconductive layer which are soluble in aqueous or alkaline solvent systems. Such binders include high-molecular-weight substances which possess groups conferring solubility in alkaline media, such as acid, anhydride, carboxyl, phenolic, sulfonic acid, sulfonamide or sulfonimide groups. Binders having high acid numbers are particularly suitable. Although these layers have good electrophotographic properties, their solubility is still inadequate for applications where very small details have to be reproduced.
There has also been disclosed a process for the production of a printing form by electrophotographic means, where a material containing an o-quinonediazide in addition to an inorganic or organic photoconductor is employed for the photoconductive layer (German Patent No. 14 47 008, equivalent to British Patent No. 996,315). The binder contained in the layer is an organic natural or synthetic resin, advantageously a mixture of polyvinyl acetate and m-cresolformaldehyde novolak. However, the interactions of the individual components of these materials are not sufficiently matched with each other so that the process has not been able to gain general acceptance.
Furthermore, it is known to incorporate substituted phenolic resins as binders into photoconductive layers used for electrophotographic recording materials in the printing industry (German Auslegeschrift 29 04 183, equivalent to British Patent No. 2,014,748). The resins are obtained by condensing aldehydes or ketones with phenols carrying relatively long-chain substituents. Due to their hydrophobic character, hydrophilic substituents must additionally be present on the phenol nucleus, such as hydroxy, amino or carboxy groups. It has, however, been found that the solubility of these layers is insufficient and that stripping is only possible to a limited extent and using strongly basic stripping agents.
On the other hand, mixtures are known which contain photosensitive compounds, such as o-quinonediazides, and phenol condensates, such as novolaks. Upon exposure to UV light, their solubility in aqueous-alkaline solutions changes due to decomposition reactions of the photosensitive compounds. It is also possible to use polymers or copolymers possessing vinyl phenol units instead of the novolak component (German Patent No. 23 22 230, equivalent to U.S. Pat. No. 3,869,292). The publication does not mention the suitability of the mixtures for electrophotographic applications.
It is also known to employ mixtures of photosensitive compounds and poly(p-vinyl phenol) as binders for photosensitive layers which are suitable for electron beam irradiation. If they contain bromine-substituted compounds, mixtures of this type in particular undergo crosslinking reactions upon exposure and are thus suitable for negative-working photoimaging processes (IBM Technical Disclosure Bulletin, Vol. 23, No. 2, July 1980, p. 773; European Patent No. 0,045,639).